The present invention relates to a method of producing 1-menthyl-.alpha.-D-glucopyranoside.
Menthol has widely been used in pharmaceuticals, foods, tooth-pastes, other mouth refreshing and cooling agents due to such peppermint flavors providing unique mouth-refreshing and cooling functions. Menthol has a problem in decreasing peppermint flavors over time due to its sublimation property. Since menthol is also water-insoluble, in the prior art it is required that menthol in use is admixed in the form of solid particles or suspended with an emulsifier, or dissolved in an organic solvent such as alcohols.
In Japanese patent publication No. 51-105, it is disclosed that, in order to overcome the above problems, menthol glycoside is used, which has a bonding structure of menthol with oligosaccharide. This menthol glycoside is highly water-soluble and exhibits no peppermint flavor of menthol. Notwithstanding, menthol glycoside may be hydrolyzed with various kinds of carbohydrase or acids to be decomposed into menthol and sugars, whereby the peppermint flavor with refreshing and cooling feelings of menthol appears, which is disclosed in 1979 Agric. Biol. Chem. Vol. 43, p. 307 and also in 1981 "Essence" No. 130, 79.
Since menthol glycoside is water-soluble and has non-sublimation property, it is unnecessary to seal menthol glycoside from atmosphere for storage differently from menthol. Menthol glycoside is so highly stable as a chemical substance that menthol glycoside shows no chemical change even leaving the same alone without sealing. Further, menthol glycoside is easily controllable for displaying refreshing and cooling feelings of menthol and pharmaceutical functions by optimization or adjustment of decomposition rate so that menthol glycoside continuously or temporary displays the same.
Menthol glycoside is usable in various foods or as mouth-refreshing and cooling agents and tobacco's flavor improver and taste in order to act as a chemical stabilizer to continue the refreshing and cooling feelings In Japanese laid-open patent publication No. 62-161716, it is disclosed to apply menthol glycoside to toothpaste compositions. In Japanese laid-open patent publication No. 6-329528, it is disclosed to apply menthol glycoside to cosmetics to keep refreshing and cooling feelings for long time. In Japanese laid-open patent publication No. 5-219929, it is disclosed to apply menthol glycoside to tobaccos for improvement in flavor and taste.
Japanese patent publication No. 51-105 also discloses methods of producing menthol glycoside, for example, a method of organically synthesizing glucose with menthol to form menthyl-glycoside as well as an organic synthesis method using acetyl-glucose or acetopromo-glucose. In 1979 Agric. Biol. Chem. Vol 43, p. 307 and also in 1981 "Essence" No. 130, 79, there are disclosed a method of catabolism of menthyl-tetraacetyl .beta.-glucopyranoside to synthesize menthyl-.alpha.-D-glucopyranoside or a method of organic synthesis of various kinds of menthol glycoside.
The above conventional methods utilize expensive catalysts and many reaction processes, resulting in high manufacturing costs. Further, in order to apply menthol glycoside to foods, it is required to completely remove organic synthesis reagent therefrom.
The present inventors had developed a conventional method of producing menthol glycoside without any expensive catalyst and many reaction processes to produce a highly safe product, wherein .alpha.-glucosidase is used to cause an enzyme reaction between a substrate of sugars such as sucrose and maltose and an acceptor of menthol, thereby to form menthol glycoside. This conventional method is disclosed in Japanese laid-open patent publication No. 9-224693. In accordance with this conventional method, menthol glycoside may be produced through a single reaction process without use of any organic synthesis reagent which is harmful for the human body or health. This conventional method is disadvantageous in too low yield to be practiced. If no surfactant is added, then the yield of produced menthol glycoside to used menthol is only about 5% in molar ratio. Even if a surfactant is added, then the yield is still low about 9%. Those yields are insufficient for practicing the above conventional method.
In the above circumstances, it had been required to develop a novel method of producing 1-menthyl-.alpha.-D-glucopyranoside as a menthol glycoside at high yield without use of any expensive catalyst and many reaction steps.